A magnetic recording disk that uses at least two ferromagnetic layers separated by an AFC film is described in U.S. Pat. No. 6,280,813, which is incorporated herein by reference. Ruthenium (Ru) is the preferred material for the AFC film because it has the same hexagonal-close-packed (hcp) crystalline structure as the cobalt (Co) alloy material in the ferromagnetic layers and has the strongest reported exchange coupling.
A spin-valve (SV) GMR read head is a sandwich structure comprising two uncoupled ferromagnetic layers separated by a nonmagnetic metallic electrically conducting spacer layer, typically copper (Cu), in which the magnetization direction (magnetic moment) of one of the ferromagnetic layers is fixed or pinned, while the magnetization direction of the free or sensing ferromagnetic layer is free to rotate. The basic SV magnetoresistive sensor is described in U.S. Pat. No. 5,206,590.
A magnetic tunnel junction (MTJ) device has two ferromagnetic layers separated by a nonmagnetic electrically insulating layer, called the tunnel barrier layer, which is typically formed of alumina. One of the ferromagnetic layers is a pinned layer whose magnetization direction is oriented in the plane of the layer but is fixed or pinned so as not to be able to rotate in the presence of an applied magnetic field. The pinned ferromagnetic layer may be pinned by interface exchange biasing with an adjacent antiferromagnetic layer, while the free ferromagnetic layer has its magnetization direction capable of rotation relative to the pinned layer's magnetization direction. The tunneling current that flows perpendicularly through the insulating tunnel barrier layer depends on the relative magnetization directions of the two ferromagnetic layers. MTJ devices have applications for use as memory cells in magnetic memory arrays and as magnetoresistive read heads in magnetic recording devices.
The SV magnetoresistive sensor and MTJ device have been improved by substitution of one or both of the free and pinned ferromagnetic layers with a laminated structure comprising two ferromagnetic films antiferromagnetically exchange coupled to one another in an antiparallel orientation by an AFC film. This laminated structure is magnetically rigid so that when used as the free ferromagnetic layer the two antiparallel films rotate together. These improved SV sensors are described in U.S. Pat. Nos. 5,408,377 and 5,465,185, which are incorporated herein by reference. The MTJ device has also been improved by substitution of this type of laminated structure for the free and pinned layers, as described in U.S. Pat. Nos. 5,841,692 and 5,966,012, which are incorporated herein by reference.
Ru is also the preferred material for the AFC film in these laminated structures used in SV sensors and MTJ devices. Ru exhibits strong antiferromagnetic coupling in the limit of very thin AFC films and very strong antiferromagnetic coupling between cobalt (Co), cobalt—iron (Co—Fe) and nickel-iron (Ni—Fe) ferromagnetic films, which form the pairs of antiparallel oriented ferromagnetic films in these laminated structures.
For some magnetic device applications it is desirable to increase the antiferromagnetic exchange coupling strength above that achieved by Ru. This is the case for magnetic recording disk applications where it is known that higher moment alloy ferromagnetic layers lead to stronger antiferromagnetic exchange coupling. Thus one approach to increase the exchange coupling in magnetic recording disks is to add high moment ferromagnetic material at the interfaces of the AFC film with the ferromagnetic layers. However, this approach requires additional layers in the disk and can also increase the intrinsic media noise.
What is needed is a material for an AFC film that increases the antiferromagnetic exchange coupling between the ferromagnetic layers.